CoCl2 encapsulated in nitrogen-doped carbon hollow cubic nanobox enabling long-life and high-rate lithium storage

Abstract

The poor cycling stability and inferior rate performance impede the application of CoCl2 in lithium-ion batteries. Herein, Prussian blue analogs (Co3[Co(CN)6]2, Co-Co PBA) microcubes are coated by a layer of polydopamine (PDA). Through carbonization and chlorination, Co-Co PBA@PDA is decomposed into CoCl2 2H2O and CoCl2 6H2O encapsulated in nitrogen-doped carbon hollow cubic nanoboxes. The closed independent carbon nanobox, strong coupling effect between carbon nanobox and CoCl2, high electron-conductive and Li+-diffusive wall of the carbon nanoboxes, and large hollow interior space bring about superior lithium storage performance through their synergy. As an anode material for lithium-ion batteries, the composite can deliver considerable discharge capacity of 406 mAh g−1 at 2 A g−1 after 1500 cycles, presenting excellent cycling performance. The average discharge capacities at 0.1 and 10 A g−1 can reach 1282 and 123 mAh g−1, respectively, which exhibits high electrochemical activity and outstanding rate capability. Electrochemical kinetics analyses in combination with ex-situ material characterization demonstrate that a certain proportion of surface capacitive behavior occurs in electrochemical reaction. The diffusion of Li ions is rapid and stable. The reaction impedance is low. The composite is of good structural integrity during cycling. This work provides a significant exploration for development of high-performance transition metal chlorides in lithium-ion batteries.